1. Field of the Invention
The present invention relates to an image processing system used for a digital copying machine and a facsimile machine. More particularly, the invention relates to an image processing system with a self-diagnosis function for the processing of image data, and a method of diagnosing the image processing system.
2. Discussion of the Related Art
With the spread of personal computers and word processors, image data to be processed for copying purposes, for example, takes various forms and increases its amount in office work. In the copying machines, a further improvement of reproduced image quality is required. In addition to such simple functions as the function of producing a predetermined number of copies of an image on an original document, and the enlargement/reduction function, further complicated functions are required, such as the function to automatically rotate input image data as to be laid out in the best mode on a selected sheet of paper, the function to process the image data of an original as instructed by an operator, the function to rearrange a plurality of original documents on a single sheet of paper, and the function to output a plurality of the images of original documents in the order indicated by an operator, that is different from the order of inputting the original documents.
An example of the copying machine with a multiple of functions is the following digital copying machine. In the copying machine, an original document or documents are set on an automatic document feeder (ADF). The ADF automatically transports documents to a platen of the machine. An image input terminal (IIT) optically reads an image on the original and converts it into digital image signals, and sends the digital image signals to an image processor. The image processor processes the image data signals, or the digital image signals in various ways, compresses the processed image data, and stores the compressed image data in a memory. To output the stored image data, the machine reads the image data out of the memory, expands the image data, and transfers the expanded image data to an image output terminal (IOT). The IOT prints the image data on a sheet or sheets of paper.
To realize the functions as mentioned above, the image processing system, or the digital copying machine, is provided with various types of functions, such as enlargement, reduction, composition, erasing, movement, copying, paint-out, and resolution change. Particularly the recent machine is capable of rotating the input image data.
The image rotation technique is well known. Japanese Patent Unexamined Publication No. Hei. 3-265959 proposes inventive image processing means capable of rotating image data expressed by tone data of 4 bits per pixel.
The conventional image processing system has the following serious problems. An error, which is caused during the image processing, is found after the processed image data is visualized, that is, it is displayed or printed. When the error is found, the input image data before it is processed has frequently disappeared in the machine. To find the location where the error is caused, the image data must be input again. This greatly influences the machine productivity. Even if such image data is present, it is impossible to find the trouble-caused location in the machine. Accordingly, the possibility of error recurrence still exists in the machine.
The technique enabling the machine itself to check whether or not the compressing and expanding process of image data is normal is disclosed in Japanese Patent Unexamined Publication No. Sho. 63-174473. In this technique, reference data for test is previously prepared. To check, specific image data is compressed and the compressed data is compared with the reference data as the previously compressed specific data. If both pieces of the data are coincident with each other, the machine decides that the compressing operation of the machine is normal.
The self-diagnosis technique disclosed in the above publication, which is based on the result of comparing the compressed specific data and the reference data, is simple and reliable. However, this technique is not practical. The reason will be described hereinafter. Let us consider a case where the maximum image size that can be processed is A4, the tone data of 4 bits per pixel, and the image density is 400 pixels per inch, i.e., 400 dpi (dots per inch). The data quantity of each of the specific data and the reference data amounts to 8 Mega bytes. The self-diagnosis technique, when incorporated into the machine, brings about increase of machine cost, and takes much time for the compression process of the specific data and the comparison process of the compressed specific data with the reference data.